1,037 research outputs found
The Influence of Galaxy Environment on the Stellar Initial Mass Function of Early-Type Galaxies
In this paper we investigate whether the stellar initial mass function of
early-type galaxies depends on their host environment. To this purpose, we have
selected a sample of early-type galaxies from the SPIDER catalogue,
characterized their environment through the group catalogue of Wang et al. and
used their optical SDSS spectra to constrain the IMF slope, through the
analysis of IMF-sensitive spectral indices. To reach a high enough
signal-to-noise ratio, we have stacked spectra in velocity dispersion
() bins, on top of separating the sample by galaxy hierarchy and host
halo mass, as proxies for galaxy environment. In order to constrain the IMF, we
have compared observed line strengths to predictions of MIUSCAT/EMILES
synthetic stellar population models, with varying age, metallicity, and
"bimodal" (low-mass tapered) IMF slope (). Consistent with
previous studies, we find that increases with ,
becoming bottom-heavy (i.e. an excess of low-mass stars with respect to the
Milky-Way-like IMF) at high . We find that this result is robust
against the set of isochrones used in the stellar population models, as well as
the way the effect of elemental abundance ratios is taken into account. We thus
conclude that it is possible to use currently state-of-the-art stellar
population models and intermediate resolution spectra to consistently probe IMF
variations. For the first time, we show that there is no dependence of
on environment or galaxy hierarchy, as measured within the SDSS
fibre, thus leaving the IMF as an intrinsic galaxy property, possibly set
already at high redshift
Five dimensions of European identity: A contribution to the italian adaptation and validation of the in-group identification Scale
Recent approaches define collective identity as a multi-component construct. Nonetheless, there is a lack of research about the dimensionality of in-group identification in relation to European Identity. Leach and colleagues (2008) proposed a framework of in-group identification, in which they distinguish five main components integrated into two higher-order dimensions. In two studies we examined the validity of the Italian version of the In-Group Identification Scale by Leach et al., with a focus on European identity. Confirmatory factor analyses revealed that the hierarchical model of in-group identification fitted the data well (Study 1); the measure was shown to have satisfactory convergent and divergent validity. In Study 2, the relations between European identification and several possible antecedents and outcomes were examined
On the shape and evolution of a cosmic ray regulated galaxy-wide stellar initial mass function
In this paper, we present a new derivation of the shape and evolution of the
integrated galaxy-wide initial mass function (IGIMF), incorporating explicitly
the effects of cosmic rays (CRs) as regulators of the chemical and thermal
state of the gas in the dense cores of molecular clouds. We predict the shape
of the IGIMF as a function of star formation rate (SFR) and CR density, and
show that it can be significantly different with respect to local estimates. In
particular, we focus on the physical conditions corresponding to IGIMF shapes
that are simultaneously shallower at high-mass end and steeper at the low-mass
end than a Kroupa IMF. These solutions can explain both the levels of
-enrichment and the excess of low-mass stars as a function of stellar
mass, observed for local spheroidal galaxies. As a preliminary test of our
scenario, we use idealized star formation histories to estimate the mean IMF
shape for galaxies of different stellar mass. We show that the fraction
of low-mass stars as a function of galaxy stellar mass predicted by these mean
IMFs agrees with the values derived from high-resolution spectroscopic surveys.Comment: 8 pages, 5 figures, MNRAS accepte
Strong Gravitational Lensing and the Stellar IMF of Early-type Galaxies
Systematic variations of the IMF in early-type galaxies, and their connection
with possible drivers such as velocity dispersion or metallicity, have been
much debated in recent years. Strong lensing over galaxy scales combined with
photometric and spectroscopic data provides a powerful method to constrain the
stellar mass-to-light ratio and hence the functional form of the IMF. We
combine photometric and spectroscopic constraints from the latest set of
population synthesis models of Charlot & Bruzual, including a varying IMF, with
a non-parametric analysis of the lens masses of 18 ETGs from the SLACS survey,
with velocity dispersions in the range 200-300 km/s. We find that very
bottom-heavy IMFs are excluded. However, the upper limit to the bimodal IMF
slope (, accounting for a dark matter fraction of 20-30%,
where corresponds to a Kroupa-like IMF) is compatible at the
level with constraints imposed by gravity-sensitive line strengths. A
two-segment power law parameterisation of the IMF (Salpeter-like for high
masses) is more constrained (, where is the power
index at low masses) but requires a dark matter contribution of
to reconcile the results with a Salpeter IMF. For a standard Milky Way-like IMF
to be applicable, a significant dark matter contribution is required within
. Our results reveal a large range of allowed IMF slopes, which, when
interpreted as intrinsic scatter in the IMF properties of ETGs, could explain
the recent results of Smith et al., who find Milky Way-like IMF normalisations
in a few massive lensing ETGs.Comment: Accepted for publication in MNRAS, 18 pages, 12 figures, 4 table
Radial variations in the stellar initial mass function of early-type galaxies
The hypothesis of a universal initial mass function (IMF) -- motivated by
observations in nearby stellar systems -- has been recently challenged by the
discovery of a systematic variation of the IMF with the central velocity
dispersion, {\sigma}, of early-type galaxies (ETGs), towards an excess of
low-mass stars in high-{\sigma} galaxies. This trend has been derived so far
from integrated spectra, and remains unexplained at present. To test whether
such trend depends on the local properties within a galaxy, we have obtained
new, extremely deep, spectroscopic data, for three nearby ETGs, two galaxies
with high {\sigma} (~300 km/s), and one lower mass system, with {\sigma} ~ 100
km/s. From the analysis of IMF-sensitive spectral features, we find that the
IMF depends significantly on galactocentric distance in the massive ETGs, with
the enhanced fraction of low-mass stars f mostly confined to their central
regions. In contrast, the low-{\sigma} galaxy does not show any significant
radial gradient in the IMF, well described by a shallower distribution,
relative to the innermost regions of massive galaxies, at all radii. Such a
result indicates that the IMF should be regarded as a local (rather than
global) property, and suggests a significant difference between the formation
process of the core and the outer regions of massive ETGs.Comment: 17 pages, 13 figures. Accepted for publication in MNRA
MUSE observations of M87: radial gradients for the stellar initial-mass function and the abundance of Sodium
Based on MUSE integral-field data we present evidence for a radial variation
at the low-mass end of the stellar initial-mass function (IMF) in the central
regions of the giant early-type galaxy NGC4486 (M87). We used state-of-the-art
stellar population models and the observed strength of various IMF-sensitive
absorption-line features to solve for the best low-mass tapered "bimodal" form
of the IMF, while accounting also for radial variations in stellar metallicity,
the overall -elements abundance, and the abundance of individual
elements such as Ti, O, Na and Ca. Our analysis reveals a strong IMF gradient
in M87, corresponding to an exceeding fraction of low-mass stars compared to
the case of the Milky Way toward the center of M87 that drops to nearly
Milky-way levels by 0.4 . This IMF gradient is found to correlate well
with both the radial profile for stellar metallicity and for -elements
abundance but not with stellar velocity dispersion. Such IMF variations
correspond to over a factor two increase in stellar mass-to-light M/L ratio
compared to the case of a Milky-way like IMF, consistent with other
investigations into IMF gradients in early-type galaxies, including recent
dynamical constraints on M/L radial variations in M87 by Oldham & Auger. In
addition to constraining the IMF in M87 we also looked into the abundance of
Sodium, which turned up to be super-Solar over the entire radial range of our
MUSE observations and to exhibit a considerable negative gradient. These
findings suggest an additional role of metallicity in boosting the Na-yields in
the central, metal-rich regions of M87 during its early and brief
star-formation history. Our work adds the case of M87 to the few objects that
as of today have radial constraints on their IMF or [Na/Fe] abundance, while
also illustrating the accuracy that MUSE could bring to this kind of
investigations.Comment: 17 pages, 13 figures, re-submitted for publication on MNRAS following
the referee's comment
Constraints on feedback processes during the formation of early-type galaxies
Galaxies are found to obey scaling relations between a number of observables.
These relations follow different trends at the low- and the high-mass ends. The
processes driving the curvature of scaling relations remain uncertain. In this
letter, we focus on the specific family of early-type galaxies, deriving the
star formation histories of a complete sample of visually classified galaxies
from SDSS-DR7 over the redshift range 0.01<z<0.025, covering a stellar mass
interval from 10^9 to 3 x 10^11 Msun. Our sample features the characteristic
"knee" in the surface brightness vs. mass distribution at Mstar~3 x 10^10 Msun.
We find a clear difference between the age and metallicity distributions of the
stellar populations above and beyond this knee, which suggests a sudden
transition from a constant, highly efficient mode of star formation in
high-mass galaxies, gradually decreasing towards the low-mass end of the
sample. At fixed mass, our early-type sample is more efficient in building up
the stellar content at early times in comparison to the general population of
galaxies, with half of the stars already in place by redshift z~2 for all
masses. The metallicity-age trend in low-mass galaxies is not compatible with
infall of metal-poor gas, suggesting instead an outflow-driven relation.Comment: 12 pages,3 figures, accepted for publication in ApJ
Consumer Intention to Buy Electric Cars: Integrating Uncertainty in the Theory of Planned Behavior
The EU’s political agenda has included among its priorities the issue of sustainable mobility, with the aim of curbing CO2 emissions and reducing air pollution. This objective implies the introduction into the EU car market of low-polluting cars, such as cars powered by an electric battery (BEV). The current research was guided by the theory of planned behavior (TPB). The intention to buy a BEV has been measured, as well as the major TPB constructs, namely attitudes, subjective norm, and perceived behavioral control. In addition, we were interested to understand the influence of individuals’ uncertainty on the intention to buy a BEV. Data collected through an online survey (N = 335) were analyzed by means of a multiple mediation model, involving the three TPB constructs as parallel mediators. Results show that (1) attitude (β = 0.67), subjective norm (β = 0.23), and perceived behavioral control (β = 0.22) significantly predict the intention to buy BEVs; (2) uncertainty has a significant negative indirect effect (b = −0.03) on intention via perceived behavioral control. Results are discussed in relation to previous research and possible practical implications
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